Embodiments of the invention relate generally to structures and methods for packaging semiconductor devices and, more particularly, to a semiconductor device package adhesive that provides stable high voltage electrical operation.
As integrated circuits become increasingly smaller and yield better operating performance, packaging technology for integrated circuit (IC) packaging has correspondingly evolved from leaded packaging to laminated-based ball grid array (BGA) packaging and eventually to chip scale packaging (CSP). Advancements in IC chip packaging technology are driven by ever-increasing needs for achieving better performance, greater miniaturization, and higher reliability. New packaging technology has to further provide for the possibilities of batch production for the purpose of large-scale manufacturing thereby allowing economy of scale.
Some semiconductor devices and packages include high voltage power semiconductor devices that are used as switches or rectifiers in power electronic circuits, such as switched mode power supplies, for example. Most power semiconductor devices are only used in commutation mode (i.e., they are either on or off), and are therefore optimized for this. Many power semiconductor devices are used in high voltage power applications and are designed to carry a large amount of current and support a large voltage.
In use, some high voltage power semiconductor devices are connected to an external circuit by way of a power overlay (POL) packaging and interconnect system, with the POL package also providing a way to remove the heat generated by the device and protect the device from the external environment. A standard POL manufacturing process typically begins with placement of one or more power semiconductor devices onto a dielectric layer by way of an adhesive. Metal interconnects (e.g., copper interconnects) are then electroplated onto the dielectric layer to form a direct metallic connection to the power semiconductor device(s). The metal interconnects may be in the form of a low profile (e.g., less than 200 micrometers thick), planar interconnect structure that provides for formation of an input/output (I/O) system to and from the power semiconductor device(s).
Inherent to some packaging technologies is the use of high-voltage switches or assemblies typically having a length of five centimeters or more. Typically such switches include a trapezoidal cross-section or profile that is affixed to a base or supporting material such as kapton, then electrically connected to other components within an assembly. The trapezoidal cross-section includes a pair of parallel surfaces, and a pair of non-parallel surfaces that are opposite one another. Typically, one of the parallel surfaces includes a surface of switches that is adhered to, for instance, the kapton, and the other of the parallel surfaces includes a ground or power plane.
In order to avoid warpage and protect the high-voltage assembly from external influences, an encapsulant is often applied, which is then laser ablated in order to electrically connect to the ground or power plane. However, because of thermal effects, water absorption, and the like, such an assembly is prone to warpage. Further, because the encapsulant also typically includes voids or may be applied either too thinly or too thickly, corona discharge and sparking can occur during high-voltage operation, which can lead to performance degradation and early life failure.
And, with respect to providing dielectric isolation between the anode and cathode junctions, a high dielectric material that is capable of providing a high reverse breakdown voltage (e.g., up to 10 kV) is typically provided for the semiconductor diode. However, such dielectric materials often have an increased thickness that may be incompatible with certain POL packaging techniques for the semiconductor diode and, if the thickness is not properly controlled, can lead to increased parasitic inductance.
Accordingly, there is a need for a simplified method for encapsulating high-voltage switches and assemblies, and for an improved adhesive.